Ferritic stainless steel sheet

ABSTRACT

A ferritic stainless steel sheet is provided. The ferritic stainless steel includes, in mass %, C: 0.020% or less, Si: 0.05 to 0.50%, Mn: 0.05 to 0.50%, P: 0.040% or less, S: 0.030% or less, Al: 0.001 to 0.150%, Cr: 18.0 to 25.0%, Ti: 0.01 to 0.50%, Ca: 0.0001 to 0.0015%, O (oxygen): 0.0015 to 0.0040%, and N: 0.025% or less, with the balance being Fe and incidental impurities. The ferritic stainless steel sheet further satisfies formula (1), below: 0.5≤PBI≤20.0 . . . (1) (where PBI=(7Al+2Ti+Si+10Zr+130Ca)×O (oxygen)×1000, and Al, Ti, Si, Zr, Ca, and O (oxygen) in the formula each represent a content [mass %] of a corresponding element in the ferritic stainless steel sheet, and the content of an element not included in the ferritic stainless steel sheet is 0).

CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. National Phase application of PCT/JP2017/006973, filedFeb. 24, 2017, which claims priority to Japanese Patent Application No.2016-065695, filed Mar. 29, 2016, the disclosures of these applicationsbeing incorporated herein by reference in their entireties for allpurposes.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a ferritic stainless steel sheet. Inparticular, the present invention relates to a ferritic stainless steelsheet that has excellent weld penetration characteristics and which haslow susceptibility to exfoliation of black spots on the weld bead duringbending.

BACKGROUND OF THE INVENTION

Ferritic stainless steel sheets are less costly and have better pricestability than austenitic stainless steel sheets, which contain a highamount of Ni. Furthermore, ferritic stainless steel sheets haveexcellent corrosion resistance and are thus used in a variety ofapplications, such as building materials, transport equipment, homeappliances, and kitchen equipment.

Among ferritic stainless steel sheets there is a Ti-stabilized ferriticstainless steel sheet, which includes Ti, a stabilizing element.Containing Ti results in formation of Ti carbonitride in the steel,which reduces dissolved C and dissolved N, and also promotes developmentof a {111} recrystallization texture. As a result, the steel sheet hasexcellent workability. When a Ti-stabilized ferritic stainless steelsheet is subjected to TIG welding (Tungsten Inert Gas welding), however,oxides called black spots tend to form on the weld bead even whensufficient gas shielding is provided.

Techniques for reducing the formation of black spots on the weld beadare disclosed in Patent Literature 1 and 2.

Patent Literature 1 discloses a ferritic stainless steel that achieves areduced formation of black spots. The ferritic stainless steel satisfiesa BI value (3Al+Ti+0.5Si+200Ca) expressed by the steel composition being0.8 or less.

Patent Literature 2 discloses a ferritic stainless steel that achieves areduced formation of black spots. The ferritic stainless steel satisfiesthe above described BI value by the steel composition being 0.8 or less.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2010-202973

PTL 2: Japanese Unexamined Patent Application Publication No. 2012-36444

SUMMARY OF THE INVENTION

When large and thick black spots form, one problem is as follows. In thecase that the steel sheet including the weld bead is subjected tobending, black spots may exfoliate and the sites after such black spotshave exfoliated may act as initiation sites for crevice corrosion, whichmay result in deterioration of corrosion resistance. Neither of thetechnologies disclosed in Patent Literature 1 and 2 sufficientlyinhibits exfoliation, during bending, of black spots of Ti-stabilizedferritic stainless steel sheets. Furthermore, since the upper limits ofthe contents of Si, Al, Ti, and Ca, which have a deoxidizing effect, arestrictly limited, the oxygen concentration in the ferritic stainlesssteel tends to increase. Thus, oxides tend to form in the steel and, inthe process of steel sheet production, scabs and surface defects tend toform. The technologies disclosed in Patent Literature 1 and 2 pose suchproblems.

Currently, Ti-stabilized ferritic stainless steel sheets, describedabove, are widely used in household appliances in order to reduceproduct costs. On the other hand, structures of such home appliances areincreasingly complex, and accordingly, there are cases in which aTi-stabilized ferritic stainless steel sheet is applied to a portionthat is to be exposed to a severe corrosive environment after its weldzone is processed by bending. Thus, there is a need for a Ti-stabilizedstainless steel sheet that has low susceptibility to crevice corrosionattack which is caused by exfoliation of black spots even in the casethat the weld bead is processed by bending.

Aspects of the present invention are directed toward providing aferritic stainless steel sheet that has low susceptibility toexfoliation of black spots in a TIG weld zone during bending.

To address the problems described above, the present inventors conductedextensive research to inhibit exfoliation of black spots during bending.As a result, the following was found. The steel composition may bedefined to have an O (oxygen) content of not greater than a specificvalue and have a PBI value, expressed by “(7Al+2Ti+Si+10Zr+130Ca)×O(oxygen)×1000”, of not greater than a specific value. This compositionreduces the occurrence of exfoliation of black spots during bendingregardless of the ratio of the total lengths of black spots in the beaddirection to the full length of the weld bead (black spot formationlength ratio).

Also, it was found that, in the case that the O (oxygen) content or thePSI value is extremely small, the weld bead has less tendency topenetrate in the sheet thickness direction and thus the weld penetrationcharacteristics are degraded. Accordingly, the present inventorsdiscovered that, by formulating defining the steel composition to havean O (oxygen) content within a specific range and have a PBI valuewithin a specific range, good weld penetration characteristics and goodinhibition of black spot exfoliation can both be achieved. The mechanismis believed to be as follows.

During TIG welding, the black spot moves on the weld bead as if theblack spot were dragged by the electrode with increasing in size, andafter being increased to a certain size or larger, the black spot isfixed to the edge of the weld bead. In a ferritic stainless steel sheet,when the content of an element having a high affinity for oxygen or thecontent of oxygen is low, the surface tension of the molten pool thatforms during TIG welding decreases as the temperature increases. As aresult, a strong flow forms on the surface of the molten pool, in adirection from the center of the weld bead, where the temperature ishigh, to the edge of the weld bead, where the temperature is low. Withthis strong flow, outward Marangoni convection becomes active. As aresult, the black spot, in a state of being relatively small, is fixedto the bead edge. Thus, the individual black spots are thin and small,which results in a reduced occurrence of exfoliation during bending.

If the content of an element having a high affinity for oxygen or thecontent of oxygen is excessively low in a ferritic stainless steelsheet, outward Marangoni convection becomes extremely active and thusthe “depth to width” ratio of the molten pool becomes extremely small.Consequently, characteristics of weld bead penetration in the sheetthickness direction are degraded.

Further studies were conducted based on the above findings, and aspectsof the present invention were made. The object according to aspects ofthe invention is as follows.

[1] A ferritic stainless steel sheet including, in mass %, C: 0.020% orless, Si: 0.05 to 0.50%, Mn: 0.05 to 0.50%, P: 0.040% or less, S: 0.030%or less, Al: 0.001 to 0.150%, Cr: 18.0 to 25.0%, Ti: 0.01 to 0.50%, Ca:0.0001 to 0.0015%, O (oxygen): 0.0.0015 to 0.0040%, and N: 0.025% orless, with the balance being Fe and incidental impurities, the ferriticstainless steel sheet further satisfying formula (1), below.

0.5≤PBI≤20.0  (1)

(Here, PBI=(7Al+2Ti+Si+10Zr+130Ca)×O (oxygen)×1000, and Al, Ti, Si, Zr,Ca, and O (oxygen) in the formula each represent a content [mass %] of acorresponding element in the ferritic stainless steel sheet, and thecontent of an element not contained in the ferritic stainless steelsheet is 0).[2] The ferritic stainless steel sheet according to [1], furtherincluding, in mass %, at least one selected from Zr: 0.01 to 0.80%, Nb:0.01% or greater and less than 0.40%, and V: 0.01 to 0.50%.[3] The ferritic stainless steel sheet according to [1] or [2], furtherincluding, in mass %, at least one selected from Cu: 0.30 to 0.80%, Ni:0.01 to 2.50%, Co: 0.01 to 0.50%, Mo: 0.01 to 2.00%, and W: 0.01 to0.50%.[4] The ferritic stainless steel sheet according to any one of [1] to[1], further including, in mass %, at least one selected from B: 0.0003to 0.0030%, Mg: 0.0005 to 0.0100%, Y: 0.001 to 0.20%, REM (rare earthmetal): 0.001 to 0.10%, Sn: 0.01 to 0.50%, and Sb: 0.01 to 0.50%.[5] The ferritic stainless steel sheet according to any one of [1] to[4], wherein the ferritic stainless steel sheet has low susceptibilityto exfoliation of black spots in a weld zone during bending.

Aspects of the present invention provide a ferritic stainless steelsheet that has low susceptibility to exfoliation of black spots in a TIGweld zone during bending. Furthermore, the ferritic stainless steelsheet according to aspects of the present invention has excellentcharacteristics of weld bead penetration and also exhibits excellentcorrosion resistance even at its bent portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the appearance of black spots thatformed in Example No. 3, of Table 1, which will be described later.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention, including the best mode, will bedescribed below.

The ferritic stainless steel sheet according to aspects of the presentinvention satisfies the following formula (1).

0.5≤PBI≤20.0  (1)

Here, PBI=(7Al+2Ti+Si+10Zr+130Ca)×O (oxygen)×1000 (In formula (1), Al,Ti, Si, Zr, Ca, and O (oxygen) each represent the content [mass %] ofthe corresponding element in the ferritic stainless steel sheet, and thecontent of an element not contained in the ferritic stainless steelsheet is 0).

Al, Ti, Si, Zr, and Ca are elements having a particularly high affinityfor oxygen and tend to form oxides. When the product of the value of thecontents of these elements and the value of the oxygen content is large,black spots tend to exfoliate during bending. In equation (1), thecoefficients of Al, Ti, Si, Zr, and Ca are determined based on themagnitude of the influence on the characteristics of weld beadpenetration and on the magnitude of the influence that causesexfoliation of black spots during bending.

In the case that the PBI value is greater than 20.0, black spotsexfoliate during bending. To inhibit such exfoliation, the PBI value isnot greater than 20.0. In the case that the PBI value is not greaterthan 5.0, the exfoliation of black spots during bending can be furtherinhibited effectively.

In the case that the PBI value is less than 0.5, the characteristics ofweld bead penetration in the sheet thickness direction is deteriorated.Accordingly, the PBI value is not less than 0.5 in accordance withaspects of the present invention. In the case that the PBI value is 1.5or greater, the characteristics of weld bead penetration are excellent.

Furthermore, in the case that the PBI value is 1.5 or greater, goodinhibition of exfoliation of black spots during bending is achievedcompared with the case in which the PBI value is less than 1.5. This isbelieved to be due to the fact that, as described above, the weldpenetration characteristics are better in the case that the PBI value is1.5 or greater than in the case that the PBI value is less than 1.5.Thus, in accordance with aspects of the present invention, it is furtherpreferable that the PBI value be 1.5 or greater and 5.0 or less.

Next, reasons for limiting the chemical composition to theaforementioned ranges in accordance with aspects of the presentinvention will be described. The percentages indicating the chemicalcomposition of the steel are mass percentages unless otherwisespecified.

C: 0.020% or less

C is an effective element for increasing the strength of steel. Thus, itis preferable that the C content not be less than 0.001%. On the otherhand, if the C content is greater than 0.020%, corrosion resistance andworkability deteriorate significantly. Thus, the C content is notgreater than 0.020%. The C content is preferably not greater than 0.015%and more preferably not greater than 0.010%.

Si: 0.05 to 0.50%

Si is an element which is useful as a deoxidizer. This effect isobtained when the Si content is 0.05% or greater. It is preferable thatthe Si content not be less than 0.08%. If the Si content is greater than0.50%, the steel hardens and workability is deteriorated. In addition,even when the composition satisfies formula (1), black spots formed inTIG welding of a ferritic stainless steel sheet tend to exfoliate duringbending, and the sites after such exfoliation may act as initiationsites for crevice corrosion. Thus, the Si content is not greater than0.50%. The Si content is preferably not greater than 0.30% and morepreferably not greater than 0.15%.

Mn: 0.05 to 0.50%

Mn acts as a deoxidizes. This effect is obtained when the Mn content is0.05% or greater. The Mn content is preferably not less than 0.10%, morepreferably not less than 0.15%, and even more preferably not less than0.17%. If the Mn content is greater than 0.50%, precipitation andcoarsening of MnS is promoted, which causes deterioration of corrosionresistance. Thus, the Mn content is not greater than 0.50%. The Mncontent is preferably less than 0.30% and more preferably not greaterthan 0.20%.

P: 0.040% or less

P is an element that deteriorates corrosion resistance. In addition, Pdeteriorates hot workability due to segregation at grain boundaries. Forthis reason, the P content is desirably as low as possible and is thusnot greater than 0.040%. It is preferable that the P content not begreater than 0.030%. The lower limit of the P content is notparticularly specified.

S: 0.030% or less

S, together with Mn, forms precipitated MnS. Such MnS deterioratescorrosion resistance due to acting as corrosion initiation sites. Thus,the S content is desirably low and is thus not greater than 0.030%. Itis preferable that the S content not be greater than 0.020%. The Scontent is more preferably not greater than 0.010% and even morepreferably not greater than 0.005%. The lower limit of the S content isnot particularly specified.

Al: 0.001 to 0.150%

Al is an effective element for deoxidation. This effect is obtained whenthe Al content is 0.001% or greater. The Al content is preferably notless than 0.005% and more preferably not less than 0.01.0%. If the Alcontent is greater than 0.150%, formation of scales on the slab uppersurface, which produce a lubricating effect in hot rolling, is reducedand thus surface defects tend to form, which deteriorates productivity.In addition, if the Al content is greater than 0.150%, black spotsformed in TIG welding of steel sheets tend to exfoliate during bendingeven when the composition satisfies formula (1), and the sites aftersuch exfoliation may act as initiation sites for crevice corrosion.Thus, the Al content is not greater than 0.150%. The Al content ispreferably not greater than 0.100% and more preferably not greater than0.050%.

Cr: 18.0 to 25.0%

Cr is an element that enhances corrosion resistance by forming apassivation film on the surface. If the Cr content is less than 18.0%,sufficient corrosion resistance is not achieved. Thus, the Cr content isnot less than 18.0, preferably not less than 20.0%, and more preferablynot less than 20.5%. If the Cr content is greater than 25.0%, toughnesstends to be deteriorated because of the influence of the σ phase or 475°C. embrittlement. Thus, the Cr content is not greater than 25.0%. The Crcontent is preferably not greater than 23.0% and more preferably notgreater than 21.5%.

Ti: 0.01 to 0.50%

Ti is an effective element for deoxidation. Also, Ti is an effectiveelement to improve corrosion resistance, because it suppresses formationof Cr carbonitrides and Cr-depleted zones by stabilizing C and N.Furthermore, Ti improves workability by promoting development of a {111}recrystallization texture. These effects are obtained when the Ticontent is 0.01% or greater. The Ti content is preferably not less than0.05% and more preferably not less than 0.20%. If the Ti content isgreater than 0.50%, the ferritic stainless steel sheet hardens and thusbendability is deteriorated. Further, TiN acts as corrosion initiationsites, which deteriorates corrosion. In addition, if the Ti content isgreater than 0.50%, black spots formed in TIG welding of a steel sheettend to exfoliate during bending even when the composition satisfiesformula (1), and the sites after such exfoliation may act as initiationsites for crevice corrosion. For the above reasons, the Ti content isnot greater than 0.50%. The Ti content is preferably not greater than0.40% and more preferably not greater than 0.30%.

Ca: 0.0001 to 0.0015%

Ca is an effective element for deoxidation. This effect is obtained whenthe Ca content is 0.0001% or greater. The Ca content is preferably notless than 0.0002% and more preferably not less than 0.0003%. If Ca iscontained in an amount of greater than 0.0015%, black spots formed inTIG welding of a steel sheet tend to exfoliate during bending even whenthe composition satisfies formula (1), and the sites after suchexfoliation may act as initiation sites for crevice corrosion. Thus, theCa content is not greater than 0.0015%. The Ca content is preferably notgreater than 0.0010% and more preferably not greater than 0.0005%.

O (oxygen): 0.0015 to 0.0040%

O (oxygen) is an element that improves characteristics of weld beadpenetration in the sheet thickness direction in TIG welding. This effectis obtained when the O (oxygen) content is 0.0015% or greater. The O(oxygen) content is preferably not less than 0.0020% and more preferablynot less than 0.0025%. If O (oxygen) is contained in an amount ofgreater than 0.0040%, black spots formed in TIG welding of a steel sheettend to exfoliate during bending even when the composition satisfiesformula (1), and the sites after such exfoliation may act as initiationsites for crevice corrosion. Thus, the O (oxygen) content is not greaterthan 0.0040%. The O (oxygen) is preferably not greater than 0.0035% andmore preferably not greater than 0.0030%.

N: 0.025% or less

If N is contained in an amount of greater than 0.025%, corrosionresistance and workability significantly is deteriorated. Thus, the Ncontent is not greater than 0.025%. It is desirable that N be reduced asmuch as possible. The N content is preferably not greater than 0.020%and more preferably not greater than 0.015%. The lower limit of the Ncontent is not particularly specified.

While basic components have been described above, other elements,described below, can be contained in accordance with aspects of thepresent invention.

Zr: 0.01 to 0.80%

Similarly to Ti, Zr is an effective element for deoxidation. Inaddition, Zr is an element that improves corrosion resistance, since itsuppresses formation of Cr carbonitrides and Cr-depleted zones andprevent sensitization by stabilizing C and N. In order to obtain theseeffects, it is preferable that the Zr content not be less than 0.01%.The Zr content is more preferably not less than 0.02% and even morepreferably not less than 0.03%. On the other hand, if the Zr content isgreater than 0.80%, the ferritic stainless steel sheet hardens and thusbendability may be deteriorated. In addition, if the Zr content isgreater than 0.80%, black spots formed in TIG welding of a steel sheettend to exfoliate during bending even when the composition satisfiesformula (1), and this may result in initiation sites for crevicecorrosion. Thus, the Zr content is not greater than 0.80%. The Zrcontent is more preferably not greater than 0.30% and even morepreferably not greater than 0.10%.

Nb: 0.01% or greater and less than 0.40%

Similarly to Ti, Nb is an element that improves corrosion resistance,since it suppresses formation of Cr carbonitrides and Cr-depleted zonesand prevent sensitization by stabilizing. C and N. In order to obtainthis effect, it is preferable that the Nb content not be less than0.01%. The Nb content is more preferably not less than 0.03% and evenmore preferably not less than 0.05%. If the Nb content is 0.40% orgreater, the ferritic stainless steel sheet hardens and may thus havedeteriorated bendability, and in addition, the recrystallizationtemperature increases, which deteriorates productivity. Thus, it ispreferable that the Nb content be less than 0.40%. The Nb content ismore preferably not greater than 0.30% and even more preferably notgreater than 0.15%.

V: 0.01 to 0.50%

V is an element that improves the crevice corrosion resistance of theferritic stainless steel sheet. In order to obtain this effect, it ispreferable that the V content not be less than 0.01%. The V content ismore preferably not less than 0.03% and even more preferably not lessthan 0.05%. If the V content is greater than 0.50%, workability may bedeterioarated. Thus, it is preferable that the V content not be greaterthan 0.50%. The V content is more preferably not greater than 0.30% andeven more preferably not greater than 0.10%.

Cu: 0.30 to 0.80%

Cu is an element that improves corrosion resistance by strengthening thepassivation film. If Cu is contained in excessive amounts, ε-Cu tends toprecipitate, which may deteriorate corrosion resistance. Thus, it ispreferable that the Cu content be from 0.30 to 0.80%. The lower limit ofthe Cu content is more preferably not less than 0.35% and even morepreferably not less than 0.40%. The upper limit of the Cu content ismore preferably not greater than 0.50% and even more preferably notgreater than 0.45%.

Ni: 0.01 to 2.50%

Ni is an element that suppresses acid-induced anode reaction and thusmakes it possible to maintain a passive state even at a lower pH. Thatis, Ni is highly effective in improving crevice corrosion resistance andnoticeably suppresses the progress of corrosion in a state of activedissolution, and thus improves corrosion resistance. In order to obtainthis effect, it is preferable that the Ni content not be less than0.01%. The Ni content is more preferably not less than 0.05% and evenmore preferably not less than 0.10%. If the Ni content is greater than2.50%, hydrogen embrittlement cracking tends to occur at workedportions. Thus, it is preferable that the Ni content not be greater than2.50%. The Ni content is more preferably not greater than 0.80% and evenmore preferably not greater than 0.25%.

Co: 0.01 to 0.50%

Co is an element that improves the crevice corrosion resistance of theferritic stainless steel. In order to obtain this effect, it ispreferable that the Co content not be less than 0.01%. It is morepreferable that the Co content not be less than 0.10%. If the Co contentis greater than 0.50%, workability may be deterioarated. Thus, it ispreferable that the Co content not be greater than 0.50%. The Co contentis more preferably not greater than 0.30% and even more preferably notgreater than 0.15%.

Mo: 0.01 to 2.00%

Mo has the effect of improving the crevice corrosion resistance of theferritic stainless steel sheet. In order to obtain this effect, it ispreferable that the Mo content not be less than 0.01%. The Mo content ismore preferably not less than 0.10 and even more preferably not lessthan 0.30%. If the Mo content is greater than 2.00%, coarseintermetallic compounds may form, which may deterioarate toughness.Thus, it is preferable that the Mo content not be greater than 2.00%.The Mo content is more preferably not greater than 1.00% and even morepreferably not greater than 0.60%.

W: 0.01 to 0.50%

W is an element that improves the crevice corrosion resistance of theferritic stainless steel sheet. In order to obtain this effect, it ispreferable that the W content not be less than 0.01%. It is morepreferable that the W content not be less than 0.10%. If the W contentis greater than 0.50%, workability may be deteriorated. Thus, it ispreferable that the W content not be greater than 0.50%. It is morepreferable that the W content not be greater than 0.30%.

B: 0.0003 to 0.0030%

B is an element that improves hot workability and secondary workability.It is known that addition of B to a Ti-containing steel is effective. Inorder to obtain this effect, it is preferable that the B content not beless than 0.0003%. It is more preferable that the B content not be lessthan 0.0010%. If the B content is greater than 0.0030%, toughness may bedeteriorated. Thus, it is preferable that the B content not be greaterthan 0.0030%. It is more preferable that the B content not be greaterthan 0.0025%.

Mg: 0.0005 to 0.0100%

Mg acts as deoxidizer by forming a Mg oxide together with Al in moltensteel. In order to obtain this effect, it is preferable that the Mgcontent not be less than 0.0005%. It is more preferable that the Mgcontent not be less than 0.0010%. If the Mg content is greater than0.0100%, the toughness of the steel is deteriorated, which may reduceproductivity. Thus, it is preferable that the Mg content not be greaterthan 0.0100%. The Mg content is more preferably not greater than 0.0050%and even more preferably not greater than 0.0030%.

Y: 0.001 to 0.20%

Y is an element that prevents a decrease in viscosity of molten steeland improves the cleanliness of the molten steel. In order to obtainthis effect, it is preferable that the Y content not be less than0.001%. If the Y content is greater than 0.20%, workability may bedeteriorated. Thus, it is preferable that the Y content not be greaterthan 0.20%. It is more preferable that the Y content not be greater than0.10%.

REM (rare earth metal): 0.001 to 0.10%

REMs (rare earth metals: elements having atomic numbers from 57 to 71,e.g., La, Ce, and Nd) are elements that improve high-temperatureoxidation resistance. In order to obtain this effect, it is preferablethat the REM content not be less than 0.001%. It is more preferable thatthe REM content not be less than 0.005%. If the REM content is greaterthan 0.10%, surface defects may form during hot rolling. Thus, it ispreferable that the REM content not be greater than 0.10%. It is morepreferable that the REM content not be greater than 0.05%.

Sn: 0.01 to 0.50%

Sn is effective in reducing the formation of work-induced surfaceroughness composed of a deformation zone which is inevitably inducedduring rolling.

In order to obtain this effect, it is preferable that the Sn Content notbe less than 0.01%. It is more preferable that the Sn content not beless than 0.03%. If the Sn content is greater than 0.50%, workabilitymay be deteriorated. Thus, it is preferable that the Sn content not begreater than 0.50%. It is more preferable that the Sn content not begreater than 0.20%.

Sb: 0.01 to 0.50%

Similarly to Sn, Sb is effective in reducing the formation ofwork-induced surface roughness composed of a deformation zone which isinevitably induced during rolling.

In order to obtain this effect, it is preferable that the Sb content notbe less than 0.01%. It is more preferable that the Sb content not beless than 0.03%. If the Sb content is greater than 0.50%, workabilitymay be deteriorated. Thus, it is preferable that the Sb content not begreater than 0.50%. It is more preferable that the Sb content not begreater than 0.20%

The balance, other than the elements described above, is Fe andincidental impurities.

Next, a suitable method for producing the ferritic stainless steel sheetaccording to aspects of the present invention will be described.Steelmaking is performed by a known method using, for example, aconverter, an electric furnace, or a vacuum melting furnace to obtain asteel having the chemical composition described above. Next, secondaryrefining is performed by, for example, VOD (vacuum oxygendecarburization) to control the oxygen concentration. Thereafter, acontinuous casting process or an ingot casting-slabbing process isperformed to produce a steel material (slab). The steel material isheated to a temperature of 1000° C. to 1200° C. and is thereafterhot-rolled to a sheet thickness of 2.0 mm to 5.0 mm under conditionsincluding a finishing temperature of 700° C. to 1000° C. The hot-rolledsheet, produced in this manner, is annealed at a temperature of 850° C.to 1100° C. and pickled and is next cold-rolled and then subjected tocold-rolled-sheet annealing at a temperature of 800° C. to 1000° C.After cold-rolled-sheet annealing, pickling is performed for descaling.The descaled cold-rolled sheet may be subjected to skin pass rolling.

The ferritic stainless steel sheet according to aspects of the presentinvention is effectively used not only as a cold-rolled sheet product asdescribed above, but also as a hot-rolled sheet product. In addition,the ferritic stainless steel sheet according to aspects of the presentinvention is suitable for bending. Furthermore, the ferritic stainlesssteel sheet according to aspects of the present invention is suitablefor applications in which the weld zone is processed by bending. Such aweld zone may be formed by any welding method. Preferably, such a weldzone is formed by TIG welding.

EXAMPLE

Examples of the present invention will be described below. The scope ofthe present invention is not limited to the examples described below.

Steelmaking was performed to produce 100-kg ingots of ferritic stainlesssteels having chemical compositions shown in Tables 1 to 5 (the balancebeing Fe and incidental impurities). Thereafter, heating to atemperature of 1200° C. was performed and hot rolling was performed toobtain a hot-rolled sheet of 3.0 mm sheet thickness. Subsequently,annealing was performed at 1050° C. and pickling was performed by acommon method. Thereafter, cold rolling was performed to a sheetthickness of 1.0 mm, and further, annealing was performed at 900° C. andpickling was performed by a common method.

Pieces of 35 mm×200 mm were cut from the obtained cold-rolled andannealed sheet, and both sides of flat surface were dry-polished with#600 emery paper. Thereafter, the edge surface was scraped to obtaintest pieces. I-shaped groove TIG welding was performed on the obtainedtest pieces to prepare welded members. The TIG welding conditionsincluded a welding current of 70 A, a welding voltage of 11 V, and awelding speed of 40 cm/min. The shielding gas used was argon, with aflow rate of 15 L/min for the torch side and 10 L/min for the back side.

<Black Spot Exfoliation During Bending>

To evaluate black spot exfoliation during bending, bending test piecesof 30 mm×200 mm, including the weld bead, were cut from the obtainedwelded members. The test pieces were subjected to 180° tight bendingsuch that the black spot formation area was the center of bending. Onlya region including the front edge, in the bend, was cut and the frontedge of the bend was observed with an optical microscope and a scanningelectron microscope at a magnification of 120× and 3000×, respectively.Test pieces that had no exfoliation observed through either of theoptical microscopes or the scanning electron microscope were given arating of “◯” (pass: excellent), test pieces that had no exfoliationobserved through the optical microscope but had exfoliation observedthrough the scanning electron microscope were given a rating of “□”(pass), and test pieces that had exfoliation observed through bothmicroscopes were given a rating of “▴” (fail). The evaluation resultsare shown in the column “Exfoliation during bending” in Tables 1 to 5.

<Corrosion Resistance of Bent Portion with Black Spots>

To evaluate the corrosion resistance of the bent portion with blackspots, a compound cycle corrosion test was conducted on theaforementioned bending test pieces processed by bending. The endportions of the test piece were covered by vinyl tape, and thereafterthe test piece was placed in a testing apparatus, with the front edge ofthe bent portion oriented upward in the vertical direction. The testenvironment was in accordance with JASO M609-91. One cycle was asfollows: salt spray (5% NaCl), 2 h→drying (60° C.), 4 h→exposure tohumidity (50° C.), 2 h. Test pieces that had no outflow rust observedafter 10 cycles of the test were given a rating of “◯” (pass:excellent), test pieces that had no outflow rust observed at the timewhen 5 cycles of the test were completed but had outflow rust observedafter 10 cycles of the test were given a rating of “□” (pass), and testpieces that had outflow rust observed at the time when 5 cycles of thetest were completed were given a rating of “▴” (fail). The evaluationresults are shown in the column “Corrosion resistance” in Tables 1 to 5.

<Weld Penetration Characteristics>

To evaluate the characteristics of weld bead penetration in the sheetthickness direction, the bead widths of the front bead and the back beadof the aforementioned welded member were measured. Then, the bead widthof the front bead was divided by the bead width of the back bead toobtain a value (bead width of front bead/bead width of back bead value)for evaluation. Test pieces having a value of 2 or less were given arating of “◯” (pass: excellent), test pieces having a value of greaterthan 2 and not greater than 3 were given a rating of “□” (pass), andtest pieces having a value of greater than 3 were given a rating of “▴”(fail). The evaluation results are shown in the column “Weldability” inTables 1 to 5.

TABLE 1 Test Chemical composition (mass %) No. C Si Mn P S Al Cr Ti Ca O1 0.008 0.14 0.15 0.022 0.003 0.046 18.1 0.28 0.0004 0.0026 2 0.010 0.110.21 0.022 0.003 0.039 19.5 0.29 0.0005 0.0027 3 0.013 0.09 0.19 0.0240.002 0.027 21.1 0.22 0.0003 0.0028 4 0.007 0.09 0.17 0.023 0.003 0.02822.8 0.25 0.0004 0.0028 5 0.009 0.12 0.22 0.020 0.002 0.032 24.7 0.260.0004 0.0030 6 0.010 0.15 0.15 0.029 0.003 0.001 21.0 0.25 0.00030.0027 7 0.011 0.10 0.23 0.024 0.001 0.012 21.2 0.29 0.0004 0.0029 80.007 0.12 0.25 0.022 0.003 0.094 20.7 0.26 0.0005 0.0028 9 0.009 0.130.21 0.027 0.001 0.147 21.3 0.30 0.0004 0.0027 10 0.013 0.14 0.19 0.0280.001 0.042 21.8 0.02 0.0004 0.0028 11 0.009 0.12 0.16 0.027 0.003 0.02421.1 0.08 0.0004 0.0029 12 0.012 0.11 0.31 0.025 0.001 0.022 21.3 0.270.0005 0.0027 13 0.008 0.09 0.17 0.024 0.003 0.035 21.1 0.49 0.00050.0027 14 0.008 0.06 0.19 0.028 0.002 0.022 20.7 0.21 0.0004 0.0026 150.010 0.08 0.16 0.027 0.002 0.030 20.5 0.24 0.0001 0.0028 16 0.012 0.140.19 0.028 0.003 0.021 21.2 0.28 0.0005 0.0028 17 0.013 0.45 0.24 0.0220.001 0.030 21.3 0.26 0.0003 0.0029 18 0.008 0.11 0.16 0.020 0.001 0.02820.9 0.24 0.0001 0.0027 19 0.013 0.09 0.21 0.022 0.003 0.027 21.2 0.250.0002 0.0026 20 0.007 0.11 0.17 0.024 0.001 0.026 21.3 0.27 0.00090.0026 21 0.008 0.09 0.18 0.029 0.003 0.022 21.2 0.23 0.0015 0.0026 220.008 0.11 0.21 0.023 0.003 0.038 21.5 0.27 0.0003 0.0016 23 0.009 0.120.24 0.022 0.002 0.030 20.5 0.29 0.0003 0.0022 24 0.008 0.08 0.21 0.0210.002 0.033 21.3 0.21 0.0001 0.0034 25 0.011 0.09 0.15 0.028 0.001 0.02321.5 0.30 0.0002 0.0038 26 0.008 0.33 0.16 0.022 0.002 0.044 20.7 0.380.0008 0.0035 27 0.011 0.45 0.22 0.027 0.001 0.098 21.3 0.25 0.00130.0038 28 0.010 0.43 0.20 0.027 0.001 0.136 20.9 0.46 0.0014 0.0034 290.011 0.47 0.20 0.029 0.001 0.147 21.1 0.48 0.0013 0.0039 30 0.012 0.080.17 0.026 0.002 0.030 21.2 0.12 0.0002 0.0026 31 0.008 0.09 0.18 0.0300.002 0.026 21.5 0.11 0.0005 0.0022 32 0.007 0.10 0.16 0.023 0.001 0.02420.7 0.12 0.0002 0.0018 33 0.012 0.09 0.15 0.027 0.002 0.022 21.4 0.160.0002 0.0015 34 0.008 0.08 0.17 0.027 0.002 0.021 20.7 0.03 0.00030.0026 35 0.008 0.06 0.25 0.022 0.002 0.002 21.0 0.11 0.0001 0.0018Chemical composition (mass %) Exfoliation Test Other Other Other duringCorrosion No. N elements (1) elements (2) elements (3) PBI bendingresistance Weldability Remarks  1 0.011 2.8 ◯ ◯ ◯ Invention Example  20.007 2.8 ◯ ◯ ◯ Invention Example  3 0.012 2.1 ◯ ◯ ◯ Invention Example 4 0.011 2.3 ◯ ◯ ◯ Invention Example  5 0.011 2.7 ◯ ◯ ◯ InventionExample  6 0.008 1.9 ◯ ◯ ◯ Invention Example  7 0.009 2.4 ◯ ◯ ◯Invention Example  8 0.008 3.8 ◯ ◯ ◯ Invention Example  9 0.009 4.9 ◯ ◯◯ Invention Example 10 0.012 1.5 ◯ ◯ ◯ Invention Example 11 0.011 1.5 ◯◯ ◯ Invention Example 12 0.011 2.3 ◯ ◯ ◯ Invention Example 13 0.011 3.7◯ ◯ ◯ Invention Example 14 0.008 1.8 ◯ ◯ ◯ Invention Example 15 0.0092.2 ◯ ◯ ◯ Invention Example 16 0.008 2.6 ◯ ◯ ◯ Invention Example 170.010 3.5 ◯ ◯ ◯ Invention Example 18 0.008 2.2 ◯ ◯ ◯ Invention Example19 0.011 2.1 ◯ ◯ ◯ Invention Example 20 0.008 2.5 ◯ ◯ ◯ InventionExample 21 0.012 2.3 ◯ ◯ ◯ Invention Example 22 0.011 1.5 ◯ ◯ ◯Invention Example 23 0.010 2.1 ◯ ◯ ◯ Invention Example 24 0.009 2.5 ◯ ◯◯ Invention Example 25 0.012 3.3 ◯ ◯ ◯ Invention Example 26 0.013 5.3 □◯ ◯ Invention Example 27 0.012 6.9 □ ◯ ◯ Invention Example 28 0.012 8.4◯ □ ◯ Invention Example 29 0.010 10.2 □ □ ◯ Invention Example 30 0.0091.4 ◯ ◯ □ Invention Example 31 0.008 1.2 □ ◯ □ Invention Example 320.008 1.0 ◯ □ □ Invention Example 33 0.013 0.9 □ ◯ □ Invention Example34 0.012 0.8 ◯ □ □ Invention Example 35 0.010 0.6 □ □ □ InventionExample

TABLE 2 Test Chemical composition (mass %) No. C Si Mn P S Al Cr Ti Ca O36 0.009 0.11 0.16 0.023 0.001 0.021 20.9 0.30 0.0004 0.0029 37 0.0110.11 0.16 0.022 0.002 0.033 21.0 0.28 0.0002 0.0026 38 0.009 0.10 0.230.022 0.003 0.025 21.3 0.28 0.0003 0.0027 39 0.008 0.09 0.45 0.029 0.0020.031 21.3 0.24 0.0004 0.0025 40 0.011 0.11 0.16 0.028 0.003 0.029 21.00.28 0.0003 0.0027 41 0.010 0.10 0.23 0.020 0.003 0.023 20.8 0.27 0.00020.0026 42 0.008 0.11 0.24 0.023 0.003 0.037 20.7 0.20 0.0001 0.0027 430.008 0.11 0.18 0.029 0.001 0.032 20.7 0.27 0.0003 0.0028 44 0.008 0.050.25 0.024 0.003 0.001 20.9 0.20 0.0001 0.0025 45 0.011 0.15 0.24 0.0260.002 0.098 20.7 0.38 0.0014 0.0028 46 0.012 0.38 0.19 0.022 0.003 0.07321.4 0.22 0.0012 0.0035 47 0.008 0.36 0.21 0.030 0.002 0.135 21.5 0.480.0005 0.0036 48 0.012 0.29 0.19 0.028 0.001 0.042 20.6 0.38 0.00030.0038 49 0.011 0.05 0.22 0.028 0.002 0.011 20.6 0.11 0.0002 0.0028 500.003 0.06 0.25 0.022 0.001 0.014 21.0 0.02 0.0003 0.0016 51 0.010 0.080.18 0.023 0.002 0.031 21.1 0.30 0.0001 0.0027 52 0.008 0.11 0.19 0.0280.002 0.039 20.8 0.23 0.0005 0.0029 53 0.010 0.09 0.19 0.026 0.002 0.02220.6 0.24 0.0003 0.0030 54 0.010 0.10 0.24 0.028 0.001 0.035 20.7 0.210.0005 0.0028 55 0.013 0.09 0.22 0.026 0.003 0.021 21.1 0.21 0.00040.0030 56 0.010 0.09 0.17 0.027 0.002 0.021 20.7 0.28 0.0002 0.0025 570.007 0.12 0.23 0.020 0.002 0.032 21.4 0.26 0.0004 0.0028 58 0.012 0.110.16 0.029 0.002 0.036 20.6 0.27 0.0005 0.0027 59 0.013 0.11 0.17 0.0270.001 0.020 20.5 0.21 0.0003 0.0028 60 0.012 0.11 0.23 0.029 0.001 0.03721.3 0.30 0.0002 0.0028 61 0.012 0.09 0.23 0.023 0.001 0.021 21.4 0.220.0004 0.0028 62 0.011 0.12 0.24 0.021 0.002 0.025 21.1 0.27 0.00020.0027 63 0.008 0.10 0.19 0.020 0.002 0.039 21.1 0.26 0.0002 0.0028 640.009 0.08 0.20 0.028 0.001 0.027 21.4 0.23 0.0003 0.0030 65 0.010 0.090.20 0.023 0.003 0.033 20.7 0.20 0.0004 0.0026 66 0.007 0.11 0.16 0.0250.001 0.030 20.6 0.20 0.0001 0.0026 67 0.011 0.11 0.24 0.023 0.003 0.02620.7 0.25 0.0004 0.0029 Chemical composition (mass %) Exfoliation TestOther Other Other during Corrosion No. N elements (1) elements (2)elements (3) PBI bending resistance Weldability Remarks 36 0.009 Zr:0.01 2.9 ◯ ◯ ◯ Invention Example 37 0.012 Zr: 0.02 2.9 ◯ ◯ ◯ InventionExample 38 0.008 Zr: 0.03 3.2 ◯ ◯ ◯ Invention Example 39 0.013 Zr: 0.053.3 ◯ ◯ ◯ Invention Example 40 0.007 Zr: 0.09 4.9 ◯ ◯ ◯ InventionExample 41 0.010 Zr: 0.15 6.1 □ ◯ ◯ Invention Example 42 0.011 Zr: 0.289.7 ◯ □ ◯ Invention Example 43 0.012 Zr: 0.49 16.3 □ □ ◯ InventionExample 44 0.010 Zr: 0.75 19.9 □ □ ◯ Invention Example 45 0.009 Zr: 0.169.5 □ ◯ ◯ Invention Example 46 0.007 Zr: 0.22 12.9 □ □ ◯ InventionExample 47 0.011 Zr: 0.25 17.4 □ □ ◯ Invention Example 48 0.013 Zr: 0.3819.7 □ □ ◯ Invention Example 49 0.012 Zr: 0.01 1.3 □ ◯ □ InventionExample 50 0.002 Zr: 0.02 0.7 □ ◯ □ Invention Example 51 0.012 Nb: 0.122.5 ◯ ◯ ◯ Invention Example 52 0.008 Nb: 0.05 2.6 ◯ ◯ ◯ InventionExample 53 0.012 V: 0.08 2.3 ◯ ◯ ◯ Invention Example 54 0.012 V: 0.032.3 ◯ ◯ ◯ Invention Example 55 0.009 Zr: 0.06, Nb: 0.08 3.9 ◯ ◯ ◯Invention Example 56 0.009 Zr: 0.09, Nb: 0.03 4.3 ◯ ◯ ◯ InventionExample 57 0.012 Zr: 0.04, V: 0.09 3.7 ◯ ◯ ◯ Invention Example 58 0.010Zr: 0.07, V: 0.14 4.5 ◯ ◯ ◯ Invention Example 59 0.008 Zr: 0.03, Nb:0.06, 2.8 ◯ ◯ ◯ Invention Example V: 0.05 60 0.010 Zr: 0.06, Nb: 0.13,4.5 ◯ ◯ ◯ Invention Example V: 0.03 61 0.012 Cu: 0.40 2.0 ◯ ◯ ◯Invention Example 62 0.010 Ni: 0.25 2.3 ◯ ◯ ◯ Invention Example 63 0.012Co: 0.14, Mo: 2.6 ◯ ◯ ◯ Invention Example 0.31, W: 0.18 64 0.007 B:0.0013 2.3 ◯ ◯ ◯ Invention Example 65 0.012 Mg: 0.0022 2.0 ◯ ◯ ◯Invention Example 66 0.012 Sn: 0.01 1.9 ◯ ◯ ◯ Invention Example 67 0.012Y: 0.02, La: 2.4 ◯ ◯ ◯ Invention Example 0.03, Sb: 0.01

TABLE 3 Test Chemical composition (mass %) No. C Si Mn P S Al Cr Ti Ca O68 0.013 0.12 0.23 0.021 0.002 0.040 21.2 0.28 0.0003 0.0029 69 0.0110.11 0.24 0.022 0.002 0.035 20.6 0.20 0.0003 0.0026 70 0.008 0.09 0.160.030 0.002 0.033 21.0 0.24 0.0004 0.0026 71 0.011 0.10 0.23 0.025 0.0030.027 21.5 0.23 0.0003 0.0025 72 0.010 0.08 0.21 0.026 0.001 0.023 20.80.22 0.0002 0.0028 73 0.012 0.11 0.25 0.021 0.002 0.039 21.3 0.27 0.00030.0027 74 0.011 0.11 0.20 0.021 0.002 0.028 20.8 0.29 0.0005 0.0025 750.012 0.10 0.19 0.021 0.001 0.039 20.9 0.21 0.0004 0.0029 76 0.012 0.090.23 0.027 0.002 0.033 20.8 0.24 0.0002 0.0026 77 0.010 0.08 0.16 0.0280.003 0.027 21.4 0.25 0.0002 0.0027 78 0.011 0.09 0.24 0.026 0.002 0.02020.9 0.27 0.0004 0.0025 79 0.011 0.08 0.17 0.024 0.003 0.024 20.9 0.290.0002 0.0027 80 0.008 0.12 0.16 0.025 0.001 0.036 20.7 0.21 0.00040.0027 81 0.013 0.08 0.17 0.026 0.002 0.033 21.3 0.21 0.0001 0.0030 820.010 0.09 0.24 0.024 0.002 0.020 21.2 0.20 0.0003 0.0030 83 0.009 0.100.19 0.029 0.003 0.032 20.9 0.24 0.0002 0.0030 84 0.011 0.08 0.20 0.0270.002 0.030 20.8 0.27 0.0002 0.0025 85 0.012 0.12 0.24 0.029 0.002 0.03221.3 0.22 0.0003 0.0030 86 0.008 0.11 0.24 0.020 0.002 0.021 20.7 0.210.0002 0.0027 87 0.012 0.12 0.23 0.020 0.003 0.034 20.5 0.26 0.00010.0027 88 0.010 0.10 0.22 0.025 0.001 0.024 21.0 0.27 0.0003 0.0027 890.013 0.10 0.25 0.020 0.003 0.028 21.3 0.23 0.0002 0.0029 90 0.009 0.110.22 0.030 0.001 0.027 21.0 0.20 0.0002 0.0028 91 0.011 0.12 0.19 0.0210.002 0.034 20.5 0.22 0.0003 0.0028 92 0.011 0.09 0.23 0.024 0.001 0.02921.4 0.28 0.0002 0.0025 93 0.010 0.08 0.16 0.024 0.003 0.025 21.1 0.260.0002 0.0026 94 0.008 0.10 0.23 0.021 0.003 0.027 21.1 0.24 0.00040.0027 95 0.008 0.10 0.16 0.021 0.003 0.022 21.1 0.30 0.0004 0.0028 960.010 0.09 0.21 0.022 0.002 0.020 20.5 0.30 0.0001 0.0028 Chemicalcomposition (mass %) Exfoliation Test Other Other Other during CorrosionNo. N elements (1) elements (2) elements (3) PBI bending resistanceWeldability Remarks 68 0.009 Zr: 0.05 Co: 0.10 4.3 ◯ ◯ ◯ InventionExample 69 0.008 Zr: 0.10 Cu: 0.43 4.7 ◯ ◯ ◯ Invention Example 70 0.012Zr: 0.09 Cu: 0.31, Mo: 0.52 4.6 ◯ ◯ ◯ Invention Example 71 0.011 Nb:0.14 W: 0.19 2.0 ◯ ◯ ◯ Invention Example 72 0.007 Nb: 0.10 Cu: 0.45 2.0◯ ◯ ◯ Invention Example 73 0.011 Nb: 0.33 Ni: 0.12, Co: 0.45 2.6 ◯ ◯ ◯Invention Example 74 0.011 V: 0.08 Ni: 0.22 2.4 ◯ ◯ ◯ Invention Example75 0.008 V: 0.09 Cu: 0.80 2.5 ◯ ◯ ◯ Invention Example 76 0.012 V: 0.25Cu: 0.44, Ni: 0.15, 2.2 ◯ ◯ ◯ Invention Example W: 0.28 77 0.009 Zr:0.04, Nb: 0.14 Mo: 0.52 3.2 ◯ ◯ ◯ Invention Example 78 0.009 Zr: 0.06,Nb: 0.11 Cu: 0.40 3.6 ◯ ◯ ◯ Invention Example 79 0.013 Zr: 0.07, Nb:0.11 Co: 0.14, Mo: 0.48 4.2 ◯ ◯ ◯ Invention Example 80 0.007 Zr: 0.03Cu: 0.42 3.1 ◯ ◯ ◯ Invention Example 81 0.008 Zr: 0.05 Cu: 0.40, W: 0.113.7 ◯ ◯ ◯ Invention Example 82 0.011 Zr: 0.09, Nb: 0.07, Ni: 0.23 4.7 ◯◯ ◯ Invention Example V: 0.07 83 0.008 Zr: 0.03, Nb: 0.13, Cu: 0.71 3.4◯ ◯ ◯ Invention Example V: 0.06 84 0.012 Zr: 0.07, Nb: 0.08, Cu: 0.45,3.9 ◯ ◯ ◯ Invention Example V: 0.09 Ni: 0.12 85 0.012 Zr: 0.04 B: 0.00173.7 ◯ ◯ ◯ Invention Example 86 0.009 Zr: 0.09 Y: 0.046, 4.3 ◯ ◯ ◯Invention Example La: 0.020 87 0.008 Nb: 0.12 Mg: 0.0016 2.4 ◯ ◯ ◯Invention Example 88 0.010 Nb: 0.13 Sn: 0.19, 2.3 ◯ ◯ ◯ InventionExample Sb: 0.12 89 0.007 V: 0.07 Y: 0.028 2.3 ◯ ◯ ◯ Invention Example90 0.013 V: 0.08 Mg: 0.0015, 2.0 ◯ ◯ ◯ Invention Example La: 0.035 910.009 Zr: 0.06, Nb: 0.08 Ce: 0.027 4.0 ◯ ◯ ◯ Invention Example 92 0.010Zr: 0.10, Nb: 0.11 B: 0.0010, 4.7 ◯ ◯ ◯ Invention Example Y: 0.048 930.009 Zr: 0.08, V: 0.05 Sn: 0.19 4.2 ◯ ◯ ◯ Invention Example 94 0.009Zr: 0.10, V: 0.06 B: 0.0023 4.9 ◯ ◯ ◯ Invention Example Mg: 0.0012 950.011 Zr: 0.08, Nb: 0.11, Sb: 0.04 4.8 ◯ ◯ ◯ Invention Example V: 0.0796 0.010 Zr: 0.07, Nb: 0.13, Mg: 0.0030, 4.3 ◯ ◯ ◯ Invention Example V:0.05 Sn: 0.09

TABLE 4 Test Chemical composition (mass %) No. C Si Mn P S Al Cr Ti Ca O97 0.009 0.12 0.21 0.021 0.003 0.029 21.4 0.27 0.0002 0.0029 98 0.0120.08 0.22 0.024 0.003 0.027 20.6 0.28 0.0001 0.0028 99 0.009 0.08 0.210.026 0.001 0.039 20.7 0.23 0.0005 0.0027 100 0.009 0.09 0.16 0.0220.001 0.021 20.5 0.20 0.0004 0.0026 101 0.007 0.08 0.20 0.021 0.0030.034 21.5 0.27 0.0005 0.0026 102 0.012 0.10 0.16 0.022 0.001 0.024 21.00.20 0.0004 0.0025 103 0.007 0.10 0.19 0.027 0.003 0.039 21.2 0.200.0001 0.0027 104 0.012 0.11 0.18 0.020 0.002 0.038 20.8 0.29 0.00030.0030 105 0.012 0.12 0.16 0.026 0.002 0.030 20.9 0.29 0.0002 0.0025 1060.008 0.10 0.24 0.028 0.001 0.029 21.5 0.28 0.0003 0.0027 107 0.008 0.080.15 0.021 0.002 0.022 20.8 0.23 0.0004 0.0030 108 0.009 0.12 0.21 0.0290.001 0.026 21.3 0.22 0.0005 0.0027 109 0.009 0.11 0.22 0.029 0.0030.025 21.1 0.29 0.0002 0.0028 110 0.008 0.10 0.18 0.030 0.001 0.033 20.50.26 0.0004 0.0025 111 0.012 0.12 0.18 0.028 0.001 0.028 21.5 0.200.0004 0.0029 112 0.012 0.09 0.23 0.028 0.002 0.024 21.1 0.30 0.00050.0027 113 0.009 0.09 0.25 0.022 0.002 0.034 20.6 0.26 0.0004 0.0027 1140.009 0.10 0.18 0.027 0.001 0.030 21.2 0.22 0.0003 0.0029 115 0.010 0.090.17 0.025 0.002 0.028 20.7 0.21 0.0002 0.0027 Chemical composition(mass %) Exfoliation Test Other Other Other during Corrosion No. Nelements (1) elements (2) elements (3) PBI bending resistanceWeldability Remarks  97 0.011 Cu: 0.40 B: 0.0014 2.6 ◯ ◯ ◯ InventionExample  98 0.009 Ni: 0.18, Mg: 0.0025, 2.4 ◯ ◯ ◯ Invention Example W:0.30 Y: 0.052  99 0.011 Zr: 0.07 Co: 0.13 Mg: 0.0021 4.3 ◯ ◯ ◯ InventionExample 100 0.008 Zr: 0.10 Cu: 0.42 Sb: 0.13 4.4 ◯ ◯ ◯ Invention Example101 0.010 Zr: 0.10 Ni: 0.22, B: 0.0028, 5.0 ◯ ◯ ◯ Invention Example Mo:0.48 Ce: 0.027, Sn: 0.14 102 0.008 Nb: 0.12 Mo: 0.34 Y: 0.062 1.8 ◯ ◯ ◯Invention Example 103 0.009 Nb: 0.13 Cu: 0.65 Mg: 0.0020 2.1 ◯ ◯ ◯Invention Example 104 0.010 Nb: 0.06 Cu: 0.43, B: 0.0018, 3.0 ◯ ◯ ◯Invention Example Co: 0.11, Sn: 0.14 W: 0.27 105 0.008 V: 0.06 W: 0.16Y: 0.062 2.3 ◯ ◯ ◯ Invention Example 106 0.008 V: 0.10 Cu: 0.43 Mg:0.0020 2.4 ◯ ◯ ◯ Invention Example 107 0.011 V: 0.09 Ni: 0.16, B:0.0016, 2.2 ◯ ◯ ◯ Invention Example Co: 0.14, Mg: 0.00018, Mo: 0.39 Y:0.072 108 0.010 Zr: 0.04, Nb: 0.14 Cu: 0.44 Sn: 0.16 3.3 ◯ ◯ ◯ InventionExample 109 0.009 Zr: 0.08, Co: 0.11, Mg: 0.0022, 4.7 ◯ ◯ ◯ InventionExample Nb: 0.07 W: 0.28 Y: 0.048, La: 0.023 110 0.009 Zr: 0.09, V: 0.07Ni: 0.17 Sb: 0.02 4.5 ◯ ◯ ◯ Invention Example 111 0.008 Zr: 0.07, V:0.09 Cu: 0.48 B: 0.0024 4.3 ◯ ◯ ◯ Invention Example 112 0.010 Zr: 0.04,V: 0.06 Cu: 0.41, Y: 0.026, 3.6 ◯ ◯ ◯ Invention Example Mo: 0.34 Sn:0.13 113 0.013 Zr: 0.04, Nb: 0.10, Mo: 0.57 Mg: 0.0023 3.5 ◯ ◯ ◯Invention Example V: 0.07 114 0.008 Zr: 0.04, Nb: 0.11, Cu: 0.30 B:0.0014 3.4 ◯ ◯ ◯ Invention Example V: 0.08 115 0.012 Zr: 0.06, Nb: 0.05,Cu: 0.44, Y: 0.088, 3.6 ◯ ◯ ◯ Invention Example V: 0.07 Ni: 0.22, Sn:0.15, Co: 0.15 Sb: 0.21

TABLE 5 Test Chemical composition (mass %) No. C Si Mn P S Al Cr Ti Ca O116 0.010 0.11 0.24 0.020 0.003 0.155 21.1 0.24 0.0001 0.0026 117 0.0090.12 0.19 0.025 0.002 0.029 16.5 0.25 0.0003 0.0026 118 0.011 0.11 0.180.020 0.002 0.022 20.8 0.53 0.0002 0.0030 119 0.008 0.22 0.18 0.0200.002 0.038 21.1 — 0.0004 0.0029 120 0.013 0.54 0.22 0.030 0.002 0.03320.5 0.13 0.0004 0.0028 121 0.012 0.11 0.18 0.028 0.002 0.035 21.1 0.290.0018 0.0029 122 0.011 0.14 0.18 0.020 0.001 0.098 18.8 0.20 0.00010.0056 123 0.008 0.14 0.20 0.021 0.003 0.026 21.1 0.11 0.0001 0.0069 1240.009 0.06 0.18 0.029 0.002 0.011 21.4 0.16 0.0003 0.0008 125 0.013 0.110.18 0.024 0.002 0.040 20.8 0.26 0.0010 0.0014 126 0.010 0.15 0.21 0.0240.002 0.047 21.5 0.17 0.0003 0.0028 127 0.009 0.08 0.15 0.023 0.0010.031 21.1 0.10 0.0005 0.0015 128 0.013 0.15 0.22 0.025 0.001 0.036 20.80.22 0.0010 0.0029 129 0.008 0.49 0.17 0.023 0.003 0.134 21.5 0.480.0012 0.0038 130 0.002 0.08 0.23 0.029 0.001 0.002 20.5 0.03 0.00010.0016 131 0.012 0.06 0.25 0.026 0.001 0.005 21.4 0.08 0.0002 0.0015 1320.008 0.05 0.16 0.020 0.003 0.004 20.6 0.05 0.0004 0.0018 Chemicalcomposition (mass %) Other Other Other Exfoliation Test elementselements elements during Corrosion No. N (1) (2) (3) PBI bendingresistance Weldability Remarks 116 0.011 4.4 ▴ ▴ ◯ Comparative Example117 0.009 2.2 ◯ ▴ ◯ Comparative Example 118 0.010 Zr: 0.01 4.4 ▴ ▴ ◯Comparative Example 119 0.007 1.6 ◯ ▴ ◯ Comparative Example 120 0.0093.0 ▴ ▴ ◯ Comparative Example 121 0.008 Zr: 0.01 3.7 ▴ ▴ ◯ ComparativeExample 122 0.009 6.9 ▴ ▴ ◯ Comparative Example 123 0.007 3.8 ▴ ▴ ◯Comparative Example 124 0.012 Zr: 0.04 0.7 □ ◯ ▴ Comparative Example 1250.010 1.5 ◯ ◯ ▴ Comparative Example 126 0.027 2.4 ◯ ▴ ◯ ComparativeExample 127 0.008 Zr: 0.82 13.1 ▴ ▴ ◯ Comparative Example 128 0.010 Zr:0.65 21.7 ▴ ▴ ◯ Comparative Example 129 0.011 Zr: 0.32 21.8 ▴ ▴ ◯Comparative Example 130 0.001 0.3 ◯ ◯ ▴ Comparative Example 131 0.0100.4 □ ◯ ▴ Comparative Example 132 0.008 0.4 ◯ □ ▴ Comparative Example

The results obtained are shown in Tables 1 to 5. Invention Examples wereevaluated as “pass” for all “Exfoliation during bending”, “Corrosionresistance”, and “Weldability”. Furthermore, Invention Examples having aPSI value of 1.5 or greater and 5.0 or less, of all the InventionExamples, were excellent because the examples had a rating of “◯” forall of the following: evaluation of black spot exfoliation duringbending; corrosion resistance of the black spot formation area afterbending; and characteristics of weld bead penetration in the sheetthickness direction. That is, it is seen that, in those examples, noblack spots exfoliated during bending of the weld bead and thuscorrosion resistance was excellent, and further the weld bead easilypenetrated.

In Comparative Examples of Test Nos. 116, 118, 120 to 123 and 127, thecontents of Al, Ti, Si, Ca, O, and Zr were each above the range in thepresent invention. As a result, black spots exfoliated during bendingand the regions after such exfoliation had low corrosion resistance.

In Comparative Examples of Test Nos. 117 and 119, the contents of Cr andTi were each below the range in the present invention. As a result,although no black spots exfoliated during bending, the regions includingblack spots had low corrosion resistance.

In Comparative Examples of Test Nos. 124 and 125, the content of O(oxygen) was below the range in the present invention. As a result,characteristics of weld bead penetration were poor.

In Comparative Example of Test No. 126, the content of N was above therange in the present invention. As a result, although no black spotsexfoliated during bending, the regions including black spots had lowcorrosion resistance.

In Comparative Examples of Test Nos. 128 and 129, the contents of theelements were within the ranges in the present invention respectively,but the PBI value of each was greater than 20.0. As a result, blackspots exfoliated during bending and the regions after such exfoliationhad low corrosion resistance.

In Comparative Examples of Test Nos. 130 to 132, the contents of theelements were within the ranges in the present invention respectively,but the PBI value of each was less than 0.5. As a result,characteristics of weld bead penetration were poor.

INDUSTRIAL APPLICABILITY

The stainless steel sheet according to aspects of the present inventionhas excellent characteristics of weld bead penetration, has lowsusceptibility to exfoliation, during bending, of black spots that formduring welding, and has low susceptibility to occurrence of crevicecorrosion due to exfoliation of black spots. Thus, the ferriticstainless steel sheet according to aspects of the present invention issuitable for elevator inner panels, interiors, duct hoods, mufflercutters, lockers, home appliance parts, office equipment parts,automotive interior parts, automotive exhaust pipes, building materials,drain covers, marine transport containers, vessels, kitchen equipment,building interior and exterior materials, automotive parts, escalators,railway vehicles, and electrical device housing panels, for example.

1. A ferritic stainless steel sheet comprising, in mass %, C: 0.020% orless, Si: 0.05 to 0.50%, Mn: 0.05 to 0.50%, P: 0.040% or less, S: 0.030%or less, Al: 0.001 to 0.150%, Cr: 18.0 to 25.0%, Ti: 0.01 to 0.50%, Ca:0.0001 to 0.0015%, O (oxygen): 0.0015 to 0.0040%, and N: 0.025% or less,with the balance being Fe and incidental impurities, the ferriticstainless steel sheet further satisfying formula (1), below:0.5≤PBI≤20.0  (1) (where PBI=(7Al+2Ti+Si+10Zr+130Ca)×O (oxygen)×1000,and Al, Ti, Si, Zr, Ca, and O (oxygen) in the formula each represent acontent [mass %] of a corresponding element in the ferritic stainlesssteel sheet, and a content of an element not contained in the ferriticstainless steel sheet is 0).
 2. The ferritic stainless steel sheetaccording to claim 1, further comprising, in mass %, at least oneselected from Zr: 0.01 to 0.80%, Nb: 0.01% or greater and less than0.40%, and V: 0.01 to 0.50%.
 3. The ferritic stainless steel sheetaccording to claim 1 or 2, further comprising, in mass %, at least oneselected from Cu: 0.30 to 0.80%, Ni: 0.01 to 2.50%, Co: 0.01 to 0.50%,Mo: 0.01 to 2.00%, and W: 0.01 to 0.50%.
 4. The ferritic stainless steelsheet according to claim 2, further comprising, in mass %, at least oneselected from Cu: 0.30 to 0.80%, Ni: 0.01 to 2.50%, Co: 0.01 to 0.50%,Mo: 0.01 to 2.00%, and W: 0.01 to 0.50%.
 5. The ferritic stainless steelsheet according to claim 1, further comprising, in mass %, at least oneselected from B: 0.0003 to 0.0030%, Mg: 0.0005 to 0.0100%, Y: 0.001 to0.20%, REM (rare earth metal): 0.001 to 0.10%, Sn: 0.01 to 0.50%, andSb: 0.01 to 0.50%.
 6. The ferritic stainless steel sheet according toclaim 2, further comprising, in mass %, at least one selected from B:0.0003 to 0.0030%, Mg: 0.0005 to 0.0100%, Y: 0.001 to 0.20%, REM (rareearth metal): 0.001 to 0.10%, Sn: 0.01 to 0.50%, and Sb: 0.01 to 0.50%.7. The ferritic stainless steel sheet according to claim 3, furthercomprising, in mass %, at least one selected from B: 0.0003 to 0.0030%,Mg: 0.0005 to 0.0100%, Y: 0.001 to 0.20%, REM (rare earth metal): 0.001to 0.10%, Sn: 0.01 to 0.50%, and Sb: 0.01 to 0.50%.
 8. The ferriticstainless steel sheet according to claim 4, further comprising, in mass%, at least one selected from B: 0.0003 to 0.0030%, Mg: 0.0005 to0.0100%, Y: 0.001 to 0.20%, REM (rare earth metal): 0.001 to 0.10%, Sn:0.01 to 0.50%, and Sb: 0.01 to 0.50%.
 9. The ferritic stainless steelsheet according to claim 1, wherein the ferritic stainless steel sheethas low susceptibility to exfoliation of black spots in a weld zoneduring bending.